diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 141dd13db67676b1047091fdf60a9fea4306984e..81aae13c46ad85afdd1fe295f9642dc018434404 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -10,6 +10,7 @@ Python 3.5 Titan X:
   - nvidia-titan-x
   except:
   - tags
+
 Python 3.5 K40:
   script:
   - export PY_EXE=python3.5
@@ -22,6 +23,7 @@ Python 3.5 K40:
   - nvidia-k40
   except:
   - tags
+
 Python 2.7 POCL:
   script:
   - export PY_EXE=python2.7
@@ -34,6 +36,7 @@ Python 2.7 POCL:
   - pocl
   except:
   - tags
+
 Python 3.5 POCL:
   script:
   - export PY_EXE=python3.5
@@ -56,3 +59,12 @@ Documentation:
   - python3.5
   only:
   - master
+
+Flake8:
+  script:
+  - curl -L -O -k https://gitlab.tiker.net/inducer/ci-support/raw/master/prepare-and-run-flake8.sh
+  - ". ./prepare-and-run-flake8.sh boxtree test"
+  tags:
+  - python3.5
+  except:
+  - tags
diff --git a/boxtree/tree_build.py b/boxtree/tree_build.py
index 13cf28b532287bebf406b3fd373d8cb4e9f59d18..7a014cdd27c3dd4b274e0d60d7a5411bcb260e5c 100644
--- a/boxtree/tree_build.py
+++ b/boxtree/tree_build.py
@@ -943,7 +943,7 @@ class TreeBuilder(object):
 
             if knl_info.level_restrict:
                 # Avoid generating too many kernels.
-                LEVEL_STEP = 10
+                LEVEL_STEP = 10  # noqa
                 if level % LEVEL_STEP == 1:
                     level_restrict_kernel = knl_info.level_restrict_kernel_builder(
                             LEVEL_STEP * div_ceil(level, LEVEL_STEP))
diff --git a/boxtree/tree_build_kernels.py b/boxtree/tree_build_kernels.py
index ccbda9212848d57ac436bce24ab6fc708501878b..d59a9f6e1f42b9492c1f5cb3320dc5b8cc9440b8 100644
--- a/boxtree/tree_build_kernels.py
+++ b/boxtree/tree_build_kernels.py
@@ -163,6 +163,7 @@ def make_morton_bin_count_type(device, dimensions, particle_id_dtype,
 
 # }}}
 
+
 # {{{ preamble
 
 TYPE_DECL_PREAMBLE_TPL = Template(r"""//CL//
@@ -898,6 +899,7 @@ def build_level_restrict_kernel(context, preamble_with_dtype_decls,
 
 # END KERNELS IN THE LEVEL LOOP
 
+
 # {{{ nonchild srcntgt count extraction
 
 EXTRACT_NONCHILD_SRCNTGT_COUNT_TPL = ElementwiseTemplate(
@@ -1678,6 +1680,7 @@ def get_tree_build_kernel_info(context, dimensions, coord_dtype,
 
 # }}}
 
+
 # {{{ point source linking kernels
 
 # scan over (non-point) source ids in tree order